A luxury yacht has been impounded at Southampton docks after more than a ton of cocaine was found hidden "ingeniously" within its bowels in the largest Class-A drugs bust in Britain.

A specialist team of anti-smuggling officers moved in on the $1m vessel after a covert operation with the codename Parsons. The yacht was headed towards Europe from the British Virgin Islands. The cargo was so well hidden that it took officers six days to find it. They were forced to "destroy the boat to find the load" under the diving platform beneath the engine room, they said.

David Armond, deputy director of international operations for the Serious Organised Crime Agency, said the 1.2-ton cargo had a purity level of about 90 per cent and could have been sold on the streets for around £300m.

Once cut, commonly with glucose or caffeine powder, the haul would have been equivalent to seven million street deals – a third of the UK's entire annual cocaine market, Mr Armond said.